Carbon fibers are long, thin filaments of material about 0.005 to 0.010 mm in diameter and composed mostly of carbon atoms. Carbon fibers are typically produced as tows or yarns consisting of several thousands of carbon fibers. The carbon fiber tow may be used by itself or woven into a fabric. The tow or fabric is combined with epoxy or other polymer and wound or molded into shape to form various composite materials. Carbon fiber reinforced composite materials are used in many applications where light weight and high strength are needed.
In order to provide continuous lengths of carbon fiber tow, it is necessary to splice the ends. Conventional methods of splicing fiber ends include applying a coating composition onto the fiber ends, placing the coated ends in contact and drying or curing the coating to form a bonded splice. However, during subsequent manufacturing operations, the bonded area may not be compatible with the resin used to impregnate the fibers, which could also cause a local potential failure or premature failure.
Joining the ends of fibers from lengths of tow or yarn by air entanglement methods is known. In this method, the ends of the tow or yarn are overlapped with each other and an air stream is applied to the overlapped portions to cause the fibers therein to become entangled with each other. However, the fiber density at the joined portion becomes much greater than the fiber density in the main portions of the tow. In other words, the fiber density is double in the splice area. This increased bulk can damage part of the tow and may cause problems in subsequent operations. For example, in pultrusion processes, the increased bulk may have difficulty passing through the die and/or cause the resin impregnated therein not to fully penetrate the tow or not to cure completely.